Incandescible cathode



1942- v 'E. H. REERINK ETAL 2,273,763

INCANDESCIBLE CATHODE Original Filed April 15, 1955 if JZ Reel-a 727% P6. ma aZez' 71622753 73,

EY 4f Patented Feb. 17, 1942 UNITED 1 2,273,763 INOANDESCIBLE CATHODE Engbert van der Willigen,

Harmen Reerink and Paul Christiaan Eindhoven, Netherlands, as-

I signers, by mesneassignments, to Hartford National Bank and Trust Company, Hartford,

Conn, as trustee original application April 15, 1935, Serial No.

16,486. Divided and this application December 17, 1940, Serial April 17, 1934 Y i 5 Claims. (Cl.

This application is a division of our co-pending application Ser. No. 16,486, filed April 15, 1935, of which the following is a specification.

The present invention relates to activated incandescible cathodes of high electron emitting capacity and which are particularly adapted for use in large capacity fion discharge tubes.

The term ion discharge tube as used herein, is to be understood to mean a discharge tube having a gaseous filling which may be either a gas or a vapor, or a mixture of gases and/or vapors, and in which the discharge current is carried primarily by the ionized gaseous filling.

When such an ion discharge tube is destined for large capacities, its cathode must possess a large electron-emitting capacity. This is obtained by providing a coatingof a highly electron-emissive substance on the cathode, by increasing the effective electron-emitting surface, and by providing an ample supply of such highly emissive substances. constructions have been suggested, for example by using recessed or channeled cathode bodies holding a large supply of highly emissive substance. l

The present invention provides a novel construction for a cathode of high electron-emit ting capacity, which is comparatively simple and inexpensive, and which gives highly satisfactory allround results.

According to the invention, the desired results are obtained by winding around a metal core, preferably made of refractory material, a plurality of thin metal wires to form around the core a structure in which a comparatively large 1 mass and large area of highly electron-emissive substance surrounds the core and is securely retained by the turns and/or layers of the thin wire. Thereby'a very large emitting surface can be provided on the cathode with an ample sup- .ply of emissive substance, which substance at the same time firmly adheres to the cathode.

To obtain this, various It has already been suggested in U. S. Patents.

Nos. 1,718,123 and 1,177,253 to use a cathode comprising a refractory core around which is helically wound a coated thin wire. This construction comprises a wire core of a highly refractory material and surrounded by turns of a single thin wire of the same or different material, and coated with emissive substance; the wire forming a single layer on the core.

The purpose of this prior art construction was to provide a structure to which the electron-emitting substance firmly adheres. The thin helical wire was comparatively closely wound 370,538. In Germany and the electron-emitting surface compared to that of a simple coated wire was not materially increased, nor was the quantity of electronemitting substance that could be held on the cathode.

According to the present invention the thin wire is wound in a plurality of layers, or a plurality of wires are wound on top of each other. In any case there are formed slots or recesses between adjacent turns and/ or between superimposed layers adapted to hold a large amount of highly'electron-emitting substance, whereas the wire afiords for the secure support and adherence to the core of this substance.

The capillary slots or interspaces produced in this construction and filled with electron-emissive substance are particularly important in the case of ion-discharge tubes, as in such tubes the gas or vapor ions neutralize the negative space charge of the incandescent cathode and thus the emitting particles located even at considerable depths of the slots and recesses can participate in the electron emission. Furthermore, the amount of emittingsubstance can be greatly increased and an ample supply thereof is provided. Thuscathodes constructed according to the invention can be built for very high current carrying capacities,

The core wire itself may and preferably does form a helix, whereas the thin helically-wound wire surrounding the core can be applied thereto to form a plurality of layers which may be spaced in various manners. The same applies to the. application of the surrounding wire to the core, and the provision of the highly electronemitting substance thereupon; both can be achieved in various manners, examples of which will be given in the detailed description of the invention. g

In order that the invention may be clearly understood and readily carried into effect, several embodiments thereof will be described more fully with reference to theaccompanying drawing, in which:

Fig. l is an enlarged view of part of a core wire surrounded in accordance with the invention by two layers of wire constituting superimposed helices.

Fig. 2 is a side view of a cathode structure constructed in accordance with Fig. 1.

Fig. 3 is an enlarged cross-section through a portion of the cathode of Fig. 2.

Fig. 4 is an ion discharge tube using a cathode in accordance with the invention.

The manner in which the increased holding ample, of tungsten, and having a. diameter of about .1 to .5 mm., are helically wound in two superimposed layers around the core having a diameter of from about .5 to 2 mm. The wires 4 and 5 are preferably wound in opposite directions on the core I to form reverse helices, The core I with the wires 4 and 5 thereon form thus a cathode as shown in Fig. 2.

The advantage in winding successive layers in opposite directions is due to the fact that the oppositely-directed stresses in the coils provides for a better grip upon the core wire. Such arrangement of the windings also further increases the structures holding capacity for the electronemissive substance and prevents the turns from falling between turns of the preceding layer, as would be the case if successive layers were Wound in the samedirection. The layers are preferably wound with a pitch greater than is the diameter of the wire, whereby the holding capacity of the cathode is greatly increased. As a rule it is advantageous to make the pitch at least twice as large as is the diameter of the wire.

Fig. 3 is a greatly nlarged sectional View of a portion of the cathode shown in Fig. 2 whereby it will be noted that the electron-emissive substance 3 forms around the core a massive layer within which are embedded the wires 4 and 5; thus the electron-emitting substance is mechanically well secured to the core and in intimate electrical contact therewith, whereas a very large amount of electron-emitting substance is provided and a large active surface obtained.

Fig. 4 is an ion discharge tube yielding a double phase current rectified current of 6 amps.

A discharge vessel I4 contains an incandescent cathode l5 according to the invention. The electrodes are connected to conductors I1 leading to four prongs IQ of a cap l8. The discharge vessel contains a gasfilling of .7 mm. xenon.

It should be noted that in past constructions, when a thin wire coated with a highly-emissive substance was wound round a core wire it was necessary for the good adherence of the coating to use a material like nickel, to which the highlyemissive substance well adhered.

' vides a good adherence of the electron-emissive substance within the recesses, hollows and slots formed by the layer of the thin wire. In some cases, however, especially where a low cathode temperature may be used and there is no danger of the nickel fusing, the core wir as well as the In general, however, the use of nickel introduces some diswire surrounding same, may be made of a refractory metal, for example tungsten, which is provided with a nickel plating.

Thereby, depending upon the use and temperatures prevailing and the mechanical rigidity of the structure, one or more parts of the cathode structure may be provided with a nickel layer. whereas other parts may at the same time not be provided with nickel layers. Similarly some of. the parts, instead of being of a refractory metal coated with nickel, may be entirely of nickel.

In the claims by individual parts of the cathode is meant the core wire and the helix or the several helices surrounding the core.

While we have described our invention on hand of specific examples and in specific applications, we do not wish to b limited thereto, but desire the appended claims to be construed as broadly as permissible in view of the prior art.

What we claim is:

1. An incandescible cathode comprising a metal core-wire, a plurality of helically-wound wires surrounding said core-wire and spaced from each other to form interspaces, and a highly electronemissive substance carried by said wires, and at least partly filling said interspaces.

2. An incandescible cath'ode structure comprising a metal core-wire, a plurality of helically wound thin wires forming superimposed spaced layers around said core-wire, adjacent layers of said thin wires being wound in opposite directions, and a highly electron-emissive substance carried by said structure and at least partly filling the space between said layers.

3. An incandescible cathode structure comprising a metal core, a plurality of helicallywound metal wires surrounding said core and spaced from each other to form interspaces, said wires being wound with a pitch which is larger than the diameter of the wire, and a highly electron-emissive substance carried by said structure and at least partly filling said interspaces.

4. An incandescible cathode structure comprising a metal core, a plurality of helically-wound metal wires surrounding said core and spaced from each other to form interspaces, said wires being wound with a pitch at least twice the diameter of the Wire, and a highly electron-emissive substance carried by said structure, and at least partly filling said interspaces.

5. An incandescible cathode comprising a metal core-wire, a helical metal sub-wire-structure surrounding said core-wire in contacting relationship to form a plurality of winding layers separated by interspaces, at least one of said layers being formed of nickel wire, and a highly electron-emissive substance carried by said structure and at least partly filling said interspaces.

ENGBERT HARMEN REERINK. PAUL CHRISTIAAN VAN DER WILLIGFN. 

